The present disclosure relates generally to polycrystalline fuses and, more specifically to silicided polycrystalline fuses.
Fuses in an integrated circuit are used for trimming circuits as well as programming memory. One type of fuse is a polycrystalline or polysilicon fuse which is a polycrystalline material with a layer of silicide on the top. The silicon layer provides the major current path in an unprogrammed fuse since it has a lower resistance than the polycrystalline material. The fuse is programmed by applying a programming current to form an open circuit in the silicide layer. This creates a current path from the silicide through the polysilicon layer and back out the silicide. The increase of resistance is then sensed once the open circuit is created in the silicide. A typical prior art fuse is illustrated in FIGS. 1A and 1B.
The designer must balance a requirement to increase the difference in resistance between the programmed and unprogrammed fuse with the die area required for the drive transistor for programming the increased resistance programmed fuse. Since the mechanism takes place by migration of the silicide in the neck region of the fuse, it is desirable to create a larger temperature gradient. One method is to increase the size of the cathode as described in “Electrically Programmable Fuse (eFUSE) Using Electromigration And Silicides,” by C. Kothandaraman, IEEE Electron Device Letters, Vol. 23, No. 9, September 2002.
A polycrystalline fuse of the present disclosure includes a first layer of polycrystalline material on a substrate and a second layer of a silicide material on the first layer. The first and second layers are shaped to form first and second terminal portions of a first width joined along a length of the fuse by a fuse portion of a second width narrower than the first width. First and second contacts are connected to the first and second terminal portions respectively. The silicide material being discontinuous in a terminal region of the second layer along the length of the fuse. This structure increases the unprogrammed resistance and creates a large temperature gradient during programming.
As implemented, the second layer includes a third material of a higher resistance than the silicide material in one of the terminal portions and in series with the silicide material between the first and second contacts to form the discontinuity. The discontinuity or third material may be in both of the terminal portions of the second layer. The third material may be a dielectric material.
The polycrystalline material may be silicon and the silicide material may be one of cobalt silicide, titanium silicide, tantalum silicide and platinum silicide. The first and second contacts may be connected to the first and second terminal portions of the second layer.
An integrated circuit may include the present fuse and a transistor connected to one of the contacts for driving the fuse with sufficient current to program the fuse.
A method of forming the present fuse includes applying a first layer of polycrystalline material on a substrate to form first and second terminal portions of a first width joined by a fuse portion of a second width narrower than the first width. A mask is formed on the first layer with openings exposing regions of the fuses portion and most, but not all of the terminal portions of the first layer along a length of the terminal portions. A second layer of a silicide material is applied on the exposed regions of the first layer; and first and second contacts are formed to the first and second terminal regions respectively.
The contacts may be made to the second layer. The method includes covering the second layer and mask with an insulative layer and forming openings in the insulative layer to expose the terminal regions and forming the contacts in the openings of the insulative layer.
These and other aspects of the present disclosure will become apparent from the following detailed description of the disclosure, when considered in conjunction with accompanying drawings.